Generally we associate chemotaxis with smell and as we humans can hardly smell water it appears strange to call hydrotaxis as chemotaxis. How would root hair grow towards water? They must smell the moisture. The water molecules diffusing from one side in their external environment towards them must be more than from all other sides. The stimulus of water thus brings about their growth towards the waterbody.
You can see for yourself hydrotropism easily. Take a clay funnel with pores all along its circular edge. Cover it with moist filter paper on outerside. Then fill up the funnel with dry saw dust and arrange germinating seeds along the rim of the funnel. With a dropper keep wetting the germinating seeds as often as required to keep them alive. The filter paper on outerside of funnel is always kept wet. While the saw dust in funnel is kept dry. Soon you will find that the roots instead of growing downwards in the funnel, come up a little and curve and creep out of a hole to get to the filter paper soaked with water. Roots of plants growing inside hanging baskets also often show such behaviour. Tap water does not usually smell. But stream water salty water does.
Under certain conditions animals may shun the water and a part of their body or the entire organism may move away from water. Rabies is a dangerous viral disease of mammals. It is generally passed to healthy, normal animals through a rabid animal's bite. There is very severe pain in the patient suffering from rabies during the act of swallowing and therefore the rabid animals become hydrophobic. That is they are afraid of water and will run away from water.
We avoid floods, powerful jets of water, very cold sprays of water, scalding water. While we are poor in smelling water we know that fish like Salmon can retrace their migration path by detecting the "smell print" and salt concentrations of the water in the river where they hatched. For the fish taste and smell are one blended sense.
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